The present invention relates to photographic products and processes and, in particular, to diffusion transfer photographic products and processes adapted to provide relatively high resolution monochromatic images in dye developer.
U.S. Pat. No. 2,983,606 discloses and claims a method for forming color images by diffusion transfer wherein the color-providing substances are dye developers. As set forth in detail in that patent, a photosensitive element comprising an exposed photosensitive silver halide emulsion is developed by application of a liquid processing composition and an imagewise distribution of diffusible, unoxidized dye developer is formed as a function of development. At least a portion of such diffusible dye developer is transferred to an image-receiving layer positioned in superposed relationship with the silver halide emulsion. The image-receiving layer is dyed by the dye developer such that a positive color image of the developed latent image in the silver halide emulsion is formed therein. At the end of a suitable imbibition period, the image-receiving layer is separated from its superposed relationship with the silver halide emulsion to permit viewing of the color transfer image.
As disclosed in the aforementioned U.S. patent, a dye developer is a compound which contains the chromophoric system of a dye and a silver halide developing function. By "a silver halide developing function" is meant a grouping adapted to develop exposed silver halide. In the method of of color image formation described in the patent, the dye developer or, more specifically, the silver halide developing function thereof, undergoes oxidation in exposed areas of the silver halide emulsion as a consequence of development to form a product which is substantially less mobile in the processing composition than is unoxidized dye developer. In unexposed and partially exposed areas of the silver halide emulsion, the dye developer is unreacted and, thus, substantially maintains its original mobility in the processing composition so as to provide an imagewise distribution of unoxidized diffusible dye developer as a function of the point-to-point degree of exposure of the silver halide emulsion. As noted above, at least a portion of this imagewise distribution is transferred to a superposed image-receiving layer to form a positive color image therein.
Typically, film units employing dye developers as color providing substances in a diffusion transfer process and adapted for separation of the image-receiving layer subsequent to processing are comprised of a photosensitive element containing at least one silver halide emulsion layer having a dye developer associated therewith and an image-receiving element containing the image-receiving layer. The respective elements are superposed subsequent to exposure and, as they are brought into superposition, an aqueous alkaline processing composition is spread therebetween to initiate development. After suitable imbibition, the image-receiving element is stripped or peeled away from the photosensitive element. Such film units may be adapted for formation of monochromatic color images and, accordingly, contain a single silver halide-dye developer combination or they may provide multicolor images and, accordingly, contain two or more silver halide-dye developer combinations. Generally, each dye developer possesses, at least subsequent to transfer, a spectral absorption range substantially complementary to the predominant sensitivity range of its associated silver halide emulsion layer.
In such film units, it is intended that the imagewise distribution of dye developer remain substantially undisturbed during transfer to the image-receiving layer so as to substantially preserve the original correspondence between the imagewise distribution of diffusible dye developer and the developed latent image. Ideally, the dye developer should diffuse over the shortest path between the superposed silver halide and image-receiving layers, i.e., a path normal to the plane of these parallel layers. In practice, virtually all of the dye developer in the imagewise distribution does diffuse in the intended manner, thereby providing a substantial and, generally, acceptable degree of correspondence between the color transfer image and the developed latent image. Nonetheless, some lateral diffusion of dye developer, i.e., diffusion oblique to the intended path, can and, generally, does occur. The resultant disturbance of the imagewise distribution of the dye developer is manifested in the transfer image by less than optimal resolution or "edge sharpness" and imposes a limitation on the capability of the film to resolve or reproduce fine detail in the photographed object. Although not unacceptably restrictive for most applications, this limitation may render film units of the aforedescribed structure unsuitable or marginally suitable for certain specialized applications requiring relatively high resolution images, e.g., certain technical or graphic arts applications.